The present invention relates to electric devices, and ore particularly to an electric device sealing structure having a characteristic casing structure.
In a conventional electric device, there is an electromagnetic relay constructed, for example, by mounting various internal components such as an electromagnet and a contact segment on a base and then sealing the structure in a casing. In this type of electromagnetic relay, as shown in FIG. 14, a casing 100 is formed with a gate portion 101, a bleeder portion 102 and a vent portion 103. The gate portion 101 is formed for injection molding. The bleeder portion 102 is formed to discharge internal air that expanded when sealing the underside of the base. It should be noted that the bleeder portion 102 will be sealed shut to prevent cleaning water from entering the inside during a later cleaning operation. Furthermore, the vent portion provides communication between the inside and the outside of the electromagnetic relay during operation so as to improve the life of electric components. More specifically, such communication prevents problems such as the wearing of contacts due to the generation of an electric arc between the contacts or a rise in temperature upon making and breaking of the connection between the contacts.
The gate portion 101, bleeder portion 102 and vent portion 103 each have an independent function and hence are conventionally formed in the casing 100 at separate locations. More specifically, the gate portion 101 and the vent portion 103 are arranged side-by-side in a substantially central area of the top wall, while the bleeder portion 102 is located at a corner of the top wall. Because of this reason, the structure of a mold for forming the casing 100 is intricate. Such an intricate structure inhibits the smooth flow of resin, which leads to the occurrence of inconveniences such as a short shot. In particular, during heat sealing of the bleeder portion 102, which is located at a corner, it is necessary to hold the casing by a supporting jig or the like so as to prevent the casing from tilting, resulting in poor workability.
Accordingly, it is an object of the present invention to provide an electric device sealing structure which has a casing that is simple fabric with superior moldability and workability.
As means for solving the foregoing problems, the present invention provides an electric device sealing structure for sealing an electric device by covering a base carrying internal components with a casing, wherein the casing is formed with a recess toward an internal space in which none of the internal components are located, the recess is provided at its bottom with a gate portion as a resin inlet for forming the casing and with a bleeder portion which is open during a sealing operation and sealed later.
With this construction, the casing has a simplified structure, and the mold for forming the casing also has a simplified structure. This allows resin to flow smoothly in injection molding, thereby assuredly providing a casing of a desired configuration.
A vent portion which is open when the electric device is in use may be also provided at the bottom of the recess.
This feature not only allows the gate portion, the bleeder portion or the bent portion to be suitably located for their purposes, but also enables a compact arrangement of internal components within the casing, thereby reducing the size of the structure.
It is preferred that the electric device comprise an electromagnetic relay having internal components including an electromagnet portion comprising a coil winding around an iron core with an intervening spool and a yoke integrated therewith, an armature disposed on one side of the electromagnet portion, a movable contact segment and a fixed contact segment disposed on the other side, and a card disposed above the electromagnet portion for transmitting the rotation of the armature to the movable contact arm, the card being shaped as a substantially rectangular frame to define the internal space in which the recess can be accommodated.
With this feature, the internal space in which the recess is to be formed can assuredly be formed even if the casing is reduced in size as an internal surface of the casing is positioned near any internal component in the casing.